(1) Field of the Invention
The present invention relates to a process for the preparation of an alkaline earth metal aluminosilicate sintered body.
(2) Description of the Related Art
Sintered bodies of inorganic powders of alumina and the like are most widely used as electric insulators for electronic parts such as IC packages because electric characteristics and mechanical characteristics of these sintered bodies are preferable. At the present, these sintered bodies are mainly prepared by the so-called cofiring method in which an unfired molded body of an inorganic powder is printed with an electric circuit by using an electroconductive substance, the molded body is then fired and the obtained circuit-printed fired body is used as an electrically insulating material. This method, however, is defective in that since a high temperature is necessary for sintering an inorganic powder, only an expensive electroconductive substance capable of enduring a high firing temperature can be used. For example, since an alumina powder is sintered at a firing temperature higher than 1500.degree. C., if it is intended to obtain an electric circuit-printed sintered body by using the alumina powder according to the cofiring technique, an expensive electroconductive substance such as Mo, Mn or W should be used. Moreover, this expensive substance is not completely satisfactory in the electroconductivity.
Accordingly, research has been made on the preparation of sintered bodies capable of being cofired with Ag, Au, Cu and the like having a good electroconductivity. One of us previously proposed a process for preparing an anorthite type sintered body by molding a powder of a specific calcium type zeolite and firing the molded body at a temperature lower than 1000.degree. C. (see Japanese Unexamined Patent Publication No. 89-100060). Furthermore, U.S. Pat. No. 4,814,303 discloses a process for preparing a ceramic body by firing a powder of a specific zeolite at a temperature of 900.degree. to 1350.degree. C. These sintered bodies are advantageous over the conventional sintered bodies in that the manufacturing cost is low and the sintering can be carried out at lower temperatures.
However, these processes are still insufficient in that the allowance in the variation of the firing temperature is very narrow if it is intended to obtain a sintered body having a high density as close to the theoretical density as possible, and the control of the temperature at the firing step is industrially difficult. For example, the above-mentioned calcium type zeolite is not sintered if the temperature at the firing step is low, and in contrast, if the temperature at the firing step is too high, bubbles are confined in the sintered body or bubbling or swelling is caused, resulting in reduction of the yield. Accordingly, the firing temperature should be controlled within a very narrow range, for example, from 880.degree. to 900.degree. C.